The present invention relates generally to processing digital signals appearing on a bus, and more particularly to a parallel bus arrangement for allowing this to happen in an easily reconfigurable fashion in a telephone system.
In telephone systems, it is becoming more and more common to use digital signals to convey speech information. These digital signals are usually in the form of PCM (pulse code modulation) where a group of binary digits are used to digitally encode a particular range of analogue magnitude values. There digital signals are commonly transmitted in a serial fashion and are commonly processed in some fashion, while in the digital domain. In addition, data, other than digitally encoded speech, can also be conveyed.
It is also common to multiplex a plurality of such digital signals onto a single serial 6us, via a technique referred to as time division multiplexing. Two of the more methods of doing this are to multiplex either 24 or 32 channels onto a single serial bus.
It is also desirable to be able to do some signal processing to these digital signals. As an example, it may be desired to adjust the signal level on certain channels; it may be desired to detect dual tone multi-frequency (DTMF) signalling on the channels; and it may be desired to remove network echos, etc.
In prior art circuits, this processing of the digital signals has been done by extracting the signals for one channel, from a parallel time division multiplexed (TDM) bus, and then passing them to the appropriate circuits for processing. After processing, the digital signals are then returned to an appropriate timeslot (or channel) on the TDM bus. The operation of accessing the bus is under the control of a centralized control device which activates the appropriate circuit at the appropriate time for accessing the bus (i.e. to read from, or write onto, the bus). U.S. Pat. No. 4,295,008 dated Oct. 13, 1981 by A. R. Johnson et al depicts such a centralized scheme (see especially FIG. 8 of that patent and its attendant description).